EP 699648 discloses a Cr-based catalyst, which comprises a chromic salt A, an organic aluminide B, a pyrrole compound C and a 13(IIIB) chloride or 14(VIB) chloride. The best chromic salts include chromium 2-ethylhexanoate, chromium naphthenate and chromium acetylacetone. A, B and D have effect on the catalytic activity, and C influences the selectivity of 1-hexene. The selectivity of 1-hexene is 80%, and the purity is 98-99%. The advantages are that 1-hexene is used as solvent for catalyst preparation and ethylene trimerization, thus the apparatus for separation of solvent with 1-hexene and cost thereof are omitted.
EP 0608447A discloses a Cr-based catalyst composition as the catalyst for ethylene oligomerization and/or copolymerization, in which the catalyst composition contains a Cr-containing compound, a pyrrole compound, a Lewis acid and/or metal alkyl compound as an activator, and optionally a halogen source which can be either inorganic halides or various organic halides. The catalyst has high 1-hexene selectivity, but with low catalytic activity.
JP 0832519 discloses Sn(OSO2F3)2 compound is used in place of halogen source as mentioned above in EP 0608447A, thus to form a new quaternary Cr-based catalyst composition. The activity and selectivity of this composition have not been improved significantly.
U.S. Pat. No. 5,910,619 discloses 1,2,3,4,5,6-hexachlorocyclohexane is used as improver to form a quaternary catalyst composition, the catalytic activity of which is improved slightly. CN 1294109A (the title of which is a catalyst for preparing 1-hexene from ethylene oligomerization and application thereof) discloses a new catalyst system, the catalytic activity of which is improved greatly. However, these catalysts cannot meet current requirements yet. There is still a need for improving the property of catalyst so as to increase catalytic activity.
In the ethylene oligomerization as disclosed in WO2004/05647, the content of 1-octylene is at most 69.3%, and the content of 1-hexene is 10-20%.